HERBAGE YIELD AND BOTANICAL COMPOSITION OVER 20 YEARS OF A PREDOMINANTLY RYEGRASS SWARD TREATED FREQUENTLY WITH PHORATE PESTICIDE AND 3 RATES OF NITROGEN-FERTILIZER

Plots at Hurley, UK, sown to perennial ryegrass (Lolium perenne) in 1968 were given 188, 376 or 752 kg N fertilizer/ha per year. Half of each plot at the lowest and highest rate of N fertilizer was given a severe pesticide (phorate) treatment at frequent intervals. Plots were cut and their herbage yield was assessed on five occasions during each of the following 20 years. There was no indication of a long–term decline in total annual herbage yield at any rate of N fertilizer use. The severe pesticide regime enhanced yield by an average of 14.6 %/year during the first 11 years, but tended to have little effect or to reduce yields subsequently. Initially (1969) all treatment plots comprised at least 85% perennial ryegrass, but this proportion declined to between 67% (medium N) and 40% (high N) by 1989. Apart from ryegrass, the main sward components were species of the grasses Agrostis, Poa, and Elymus and traces of the broad-leaved species Stellaria media and Taraxacum officinale. © 1990, Cambridge University Press. All rights reserved.